Let us continue with our digressions on secret messages!Cryptology is the scientific discipline that gathers and studies the knowledge and techniques necessary to solve cryptograms (cryptanalysis) and to make cryptography (encrypted writing). Initially, its study was restricted to academic circles, bank security systems and military inteligence due to its application in confidential messages during war periods, State matters and espionage but, lately, it has received special attention because of the generalization of commercial operations through electronic means, where transactions must be processed secretly and safely, preferably with the lowest possible cost, since cryptographic messages consume a lot of processing time and transmission band. The oldest register of a work published on cryptanalysis comes from the Arabian philosopher Abu Yusuf Ya 'qub ibn Is-haq ibn as-Sabbah ibn 'omran ibn Ismail al-Kindi, called "A Manuscript about Decryption of Cryptographic Messages", on which he dealt about frequency analysis in encrypted texts.